This application is based upon and claims the benefit of priority of Japanese Patent Application No. 2000-325722 filed on Oct. 25, 2000 and No. 2001-74898 filed on Mar. 15, 2001, the contents of which are incorporated herein by reference.
1. Field of the Invention
The present invention relates to a flexible joint for transmitting torque from a drive device such as an engine or a power motor to a driven device such as a pump or a compressor.
2. Description of Related Art
Conventionally, as shown in FIG. 20, a pulley P (first rotor) receives torque from a driving source such as an engine. A cylindrical inner wall of the pulley P is press fitted to an outer circumference of a radial contact roller bearing Q whose inner circumference is fixed to a housing (not shown) of a driven device such as a compressor so that the pulley P is rotatably held by the driven device. An inner wall of a ring shaped damper cup Dc (second rotor) is fixed by welding to the inner wall of the pulley P. A driven rotor H (third rotor) having a center hub is fixed to a shaft (not shown) of the driven device. A damper D, which is made of elastic material such as rubber or elastmer, is accommodated in the damper cup Dc so as to be sandwiched between the damper cup Dc and the driven rotor H for absorbing a torque fluctuation. Accordingly, the torque of the pulley P is transferred to the shaft of the driven device via the damper cup Dc, the damper D and the driven rotor H.
In a case that the driven rotor has a torque limiter that serves to interrupt a torque transmission when torque applied to the flexible joint exceeds a predetermined value, it is necessary to adequately absorb a pulsating torque fluctuation, which, in particular, occurs at high speed and high load operation, for the purpose of avoiding erroneous break down of the torque limiter.
To adequately absorb the torque fluctuation, it is better to have a larger damper since, as the size of the damper is larger, its elastic coefficient (spring constant) is lower. However, to accommodate the larger damper in the second rotating body (damper cup), it is necessary to enlarge an outer wall diameter of the second rotating body since the inner wall of the second rotating body is fixed to the inner wall of the pulley, which results in enlarging an outer diameter of the pulley.
It is an object of the present invention to provide a flexible joint with a torque limiter in which torque fluctuation is successfully absorbed without enlarging a body size thereof, compared to the conventional flexible joint.
Another object of the invention is to provide a flexible joint in which an eccentric load applied thereto (load acting perpendicular to a drive or driven shaft) is not transferred from the drive shaft to a driven shaft.
It is an aspect of the present invention to provide the flexible joint a part of which is rotatably held by a housing of a drive or driven device to absorb the eccentric load.
It is another aspect of the present invention to provide the flexible joint in which first and second rubber dampers are disposed at different positions and in series between a driving device and a driven device so that a composite elastic coefficient of the dampers is smaller.
A further aspect of the present invention is to provide the flexible joint in which a second rotating body has a larger inside space for accommodating a larger damper without enlarging an outer diameter of the second rotating body.
To accomplish the above-described object, the flexible joint is composed of a first rotating body connected to a shaft of one of drive and driven devices, a second rotating body that is coaxially connected with the first rotating body and has an outer circumferential wall and an inner wall that is rotatably held by a housing of the other one of the drive and driven devices, a third rotating body connected to a shaft of the other one of the drive and driven devices, and an elastically deformable first damper through which the second rotating body is coaxially coupled with the third rotating body at a position inside the outer circumferential wall and outside the inner wall. The third rotating body is provided with a torque limiter that, when torque applied to the third rotating body exceeds a predetermined value, serves to interrupt a torque transmission from the shaft of the drive device to the shaft of the driven device via the first and second rotating body.
It is preferable that the first rotating body is a pulley whose inner circumference is connected to an outer circumference of the outer circumferential wall.
Further, as an alternative, the first rotating body may be connected to the second rotating body on a side axially opposite to the inner wall rotatably held by the other one of the drive and driven devices.
As the second rotating body is rotatably held by the other one of the drive and driven devices without sandwiching a part of the first rotating body therebetween, inner radial space of the second rotating body between the outer circumferential wall and the inner wall, where the first damper is accommodated, is larger. Accordingly, a larger size of the first damper may be employed to effectively absorb the torque fluctuation.
Preferably, an elastically deformable second damper is disposed between an outer circumference of the first rotating body and an inner circumference of the second rotating body to transfer the torque between the first and second rotating bodies. When the torque transferred from the shaft of the drive device to the shaft of the driven device, an excessive torque fluctuation is absorbed by both of the first and second dampers. Accordingly, stress occurring in each of the first and second dampers is smaller so that, while each life time of the first and second dampers is longer, an entire body of the flexible joint is more compact.
Preferably, the second rotating body is provided on the outer circumferential wall with a plurality of inward protrusions extending radially inward at given angular intervals. The third rotating body is provided on an outer circumference thereof with a plurality of outward protrusions extending radially outward at given angular intervals. The respective inward and outward protrusions are alternately positioned circumferentially so as to be overlapped radially with each other. The first damper is composed of a plurality of damper piece units circumferentially arranged between the respective inward and outward protrusions.